Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Dr. Szebellédy Lászlóné: A vízminőség szerepe és változásai csővezetékekben

Special Conference Number, Szebellédy, L. Hidrológiai Közlöny 1971. 1. sz. 53 changes in hydraulie conditions, the positive influenee of regular flushing is noted, whereas stagnation is pointedout, in agreement with other authors, as the factor most detrimental to bacterial quality. The most important external factor is the interruption of the closed network-system, which is related to the generál ageing of the pipes. Any rupture accompanied by pressure fluctuations may result in grave epidemics, due to depression. The influenee of pipe material and joint sealing on bacterial quality was investigated, and the presence of caulking materials was detected in the network. These substances and their surface offer welcome opportunity for the proliflcation of bacteria. Changes in temperature may have complex consequences, in that the seasonal proliflcation of certain bacteria may be promoted and the rate of chemical reaetions may be influenced. For example the disinfecting effect of chlorine is reduced in cold weather, while taste and other components are more volatile when warm. Summarizing the conclusions of the author it may be stated that bacterial data on network water must be interpreted statistically, preferably by classifying bacteria into categories. Sampling points in the network should be selected with care, and checks on the quality of network water can be made more reliable by increasing the number of analyses. Besides the chemical and bacterial classification of drinking waters, increasing importance is attributed to biological tests using the microscope, the aim of which is to determine the quality and quantity of micro-sediments in waters of different origin. These problems are considered in the paper by Z. Szabó. Micro-sedhnent is understood as the entity of micro-organisms, lifeless detritus and debris of both organic and inorganic origin present in natural water. Information on the micro-sediment yields an indication on the origin of drinking and industrial water, on the extent of pollution in natural surface- and groundwater, further, on the progress of biological purification in stored wastes. The efficiency of treatment facilities can be deseribed in terms of the quality and composition of micro-sediment and the changes thereof, troubles in operation can be detected, their causes may be estimated, moreover variations in flow-conditions, stagnation, etc., may be observed. Such investigations yield accurate information on toxic effects and on the extent of disinfection. The conditions of clogging and incrustation must be understood in distribution networks, since changes in the taste, odour and sometimes colour of water are mostly due to the influenee of micro-organisms. As will be perceived from the foregoing, a suitable method is required for checking the operation of intakes, structures and networks, regardless whether of an experimentál character or realized by an up-to-date technology. The conventional physical, chemical and bacteriological methods of testing are often inadequate alone, since the data obtained do not always yield a satisfactory explanation for the relationships between cause and effect. Microsediments are always present in raw-water, but alsó in drinking—and industrial water produced by proper treatment. The quality of water can always be deseribed in terms of the quality and the composition of this micro-sediment. Biological test using the microscope invariably provide a true picture on the types of micro-organisms and on the character of bioindicators, on the quality of organic detritus and inorganic debris, as well as on the changes of their quantity. Biological judgement founded on the above investigations is practically essential for meeting quality specifications. The above conclusions are supported alsó by the papét

1 of Schiefner, Hegyessy and Pénzes. The biological quality of water has been tested at 11 water-works in Hungary, drawing on surface water; demonstrating the essential role of biological, more precisely microscopic biological testing to supplement the chemical and bacterial analysis of water. The results are especially valuable for assessing the efficiency of treatment technology and are thus important not only as eriteria for the sanitary-quality of water, but alsó as indices of technology. No treatment technology can be applied reliahly and no quality specifications can be satisfied continually, unless regular checks are performed on both the raw- and the treatedwater. Summarizing the major problems and trends of research, the difficulties arising when waters of different quality are mixed should be mentionod in the first instance. Although the problem is considered extensively in the papers submitted, it should be emphasised, that differences in quality deserving attention may occur not only where surface and subsurface water are mixed, but alsó where groundwaters of different origin are only used. Since the need for determining the method of mixing often arisies in practice, the literature on the subject is copious, and several mixing diagrams are published. It should be noted further, that the safest method for avoiding harmful effects, is to perform mixing in a basin or reservoir ratlier than in the network. Interaction between the chemical components of water and the pipe material. first of all corrosion, is the result of familiar chemical processes, deseribed alsó in numerous papers. One of the most effective control consists in the use of plastics, as mentioned in one of the papers, and gaining in popularity. Regardless of its chemical composition, water of drinking quality is harmless to plastics. According to somé Germán authors and measurements by the Research Institute for Water Resources Development, somé of the plastics,—such as soft P.V.C.—consume chlorine in small quantities. Somé of the pipe material is alsó unquestionably dissolved in water, although opinions diverge on this point. Since the limit concentration of various solvents, plasticizers, hardeners and other plastic components is very low, drinking water may easily acquire taste and odour thereform. However, even ifit is anticipated that toxic, taste and odour substances are introduced from somé plastics into drinking water, this is easy to prevent by introducing suitable material tests and standards of approval.